A. Field of the Invention
The present invention relates to mattresses of the type used to support a recumbent human. More particularly, the invention relates to novel air mattresses which use a matrix array of air bladder cells that are individually inflatable and deflatable in time varying sequences which cause quiescent support forces for a human body lying on the mattress to have superimposed thereon spatially moving, time varying traveling waves of support force which correspond to traveling waves of air pressure pulses input to the air bladder cells. The body support forces waves can be programmed to travel longitudinally, laterally or obliquely on the upper support surfaces of the air bladder cells, according to pre-determined patterns which can be used to minimize formation of decubitus sores on a patient's body and alternatively to simulate comforting motions such as floating on a rolling water wave, or rocking in a boat, which simulations may optionally be accompanied by appropriate music and/or environment-simulating sounds.
B. Description of Background Art
Pressure sores, which are also known as decubitus ulcers or bed sores occur in the outer tissues of a person's body if they are subjected to relatively large pressures and/or shear forces for long periods of time. Such sores are caused by reduction in blood circulation caused by surface force pressures which exceed the person's capillary blood pressure. The problems with bed sores forming on the skin of persons with medical conditions which require them to be in relatively immobile positions on a hospital bed or in a wheel chair can be severe, resulting in painful, difficult to treat conditions, loss of limbs, or even death.
For the foregoing reasons, hospitals, nursing homes and other such health care providers which provide care giving to ailing or elderly people are keenly aware of the necessity to carefully monitor people under their care to prevent formation of bed sores. A commonly used method to minimize the possibility of bed sore formation is to turn the patient periodically, i.e., to re-adjust the patient's position on a bed mattress or in a wheel chair so that long-term pressures can be relieved from parts of a patient's body. However, turning invariably results in renewed higher pressures on other parts of the body, so the turning process must be repeated usually at least on a daily basis.
Presumably in response to a perceived need to reduce problems of bed sore formation, a variety of devices and methods have been proposed to reduce long-term, large force or pressure concentrations on a person's body. For example, Cottner et al, in U.S. Pat. No. 5,243,723, Sep. 17, 1993, Multi-Chambered Sequentially Pressurized Air Mattress With Four Layers discloses an air mattress which has two lower layers constantly pressurized at about 1 psi gauge, and two upper layers that each have serpentinely shaped, transversely disposed interdigitated membrane areas which are cyclically and alternately pressurized with varying air pressure in a push-pull fashion which creates a standing wave of variation in support force for a patient, with the intended purpose of minimizing formation of decubitus sores. The standing waves produced by alternate inflation and deflation of adjacent interdigitated members shifts support forces up and down, leaving the average maximum reaction support force concentrations on parts of a patient's body unchanged.
The present invention was conceived of to provide air mattresses which provide traveling waves of support-forces for the body of a person supported by the mattress, which can reduce maximum force concentrations.